Polarization rotator assembly including a subwavelength composite portion

Abstract

A polarization rotator assembly for rotating a polarization mode of an electromagnetic signal is provided. The polarization rotator assembly has a waveguiding structure of co-extensive first and second layers defining, successively, an input portion, a subwavelength composite portion and a polarization rotating portion. The subwavelength composite portion is formed by the first and second layers, where the second layer defines a subwavelength pattern. The polarization rotator portion is geometrically configured to rotate the polarization mode of the electromagnetic signal.

The invention claimed is: 
     
       1. A polarization rotator assembly for rotating a polarization mode of an electromagnetic signal, the polarization rotator assembly comprising:
 a waveguiding structure having co-extensive first and second layers and having a first height corresponding to the first layer and a second height corresponding to a superposition of the first and second layers, the waveguiding structure having a waveguiding axis and comprising successively therealong: 
 an input portion formed by the first layer; 
 a subwavelength composite portion formed by the first and second layers, where the second layer defines a subwavelength pattern having a characteristic feature size which is less than half an effective wavelength of the electromagnetic signal when propagating therein; and 
 a polarization rotator portion comprising at least the first and second layers and geometrically configured to rotate a polarization mode of the electromagnetic signal. 
 
     
     
       2. The polarization rotator assembly according to  claim 1 , wherein the polarization rotator portion is configured to rotate the polarization mode of the electromagnetic signal by 90 degrees. 
     
     
       3. The polarization rotator assembly according to  claim 1 , wherein the polarization rotator portion is configured to rotate the polarization mode of the electromagnetic signal from a TM polarized mode to a TE polarized mode. 
     
     
       4. The polarization rotator assembly according to  claim 1 , wherein the first and second layers are made of silicon, silicon nitride, silicon carbide, indium phosphide, gallium arsenide, a high-index polymer or a combination thereof. 
     
     
       5. The polarization rotator assembly according to  claim 1 , wherein the subwavelength pattern comprises a series of corrugations formed by said second layer and extending transversally to the waveguiding axis, said series of corrugations being interleaved with a series of gaps. 
     
     
       6. The polarization rotator assembly according to  claim 5 , wherein the gaps of the subwavelength pattern are filled with air or with a cladding material. 
     
     
       7. The polarization rotator assembly according to  claim 5 , wherein the series of corrugations has a fixed period. 
     
     
       8. The polarization rotator assembly according to  claim 5 , wherein the series of corrugations has a variable period. 
     
     
       9. The polarization rotator assembly according to  claim 5 , wherein the series of corrugations has a fixed duty cycle. 
     
     
       10. The polarization rotator assembly according to  claim 5 , wherein the series of corrugations has a variable duty cycle. 
     
     
       11. The polarization rotator assembly according to  claim 5 , wherein the series of corrugations has an aperiodic distribution. 
     
     
       12. The polarization rotator assembly according to  claim 1 , wherein the subwavelength pattern comprises a series of corrugations formed by said second layer and extending parallel to the waveguiding axis. 
     
     
       13. The polarization rotator assembly according to  claim 1 , wherein the subwavelength pattern comprises an array of pillars formed by said second layer. 
     
     
       14. The polarization rotator assembly according to  claim 1 , wherein the subwavelength pattern comprises an array of holes extending through said second layer. 
     
     
       15. The polarization rotator assembly according to  claim 1 , wherein the subwavelength pattern comprises a wedge-shaped section forming a longitudinally widening taper along said waveguiding axis. 
     
     
       16. The polarization rotator assembly according to  claim 1 , wherein the subwavelength composite portion tapers down from a first width to a second width. 
     
     
       17. The polarization rotator assembly according to  claim 1 , wherein the waveguiding structure further comprises a buffer zone between the subwavelength composite portion and the polarization rotator portion. 
     
     
       18. The polarization rotator assembly according to  claim 1 , wherein the polarization rotator portion is formed by the first and second layers and the rotation of the polarization mode of the electromagnetic signal based on a level difference between the first and the second heights. 
     
     
       19. The polarization rotator assembly according to  claim 17 , wherein the polarization rotation portion has an input end and an output end, and wherein a width of the second layer along the waveguiding axis decreases from the input end to the output end. 
     
     
       20. The polarization rotator assembly according to  claim 18  wherein a width of the first layer along the waveguiding axis increases from the input end to the output end of the polarization rotating portion. 
     
     
       21. The polarization rotator assembly according to  claim 1 , wherein the polarization rotating portion comprises a polarization-rotating path and a polarization-maintaining path, said polarization rotating portion being geometrically configured to split the electromagnetic signal into two signal polarization components respectively guiding along the polarization rotating and maintaining paths.